This invention relates to a method of saccharifying cellulose by use of the cellulase of Clostridium thermocellum. More particularly, this invention relates to a method of saccharifying cellulose by use of the cellulase of Clostridium thermocellum wherein the saccharification is enhanced by the presence of thiol reducing agents and also by the presence of Ca.sup.2+.
There has been great interest in recent years in microbial processing of cellulosic material to provide new sources of energy, chemicals, and single-cell protein. In particular, much effort has been devoted to the conversion of native forms of cellulose to valuable fermentation products such as ethanol. The rate-limiting step in this process is the depolymerization of cellulose to sugars, known as saccharification. This limitation is imposed to various extents by the proportion of cellulose which is in the crystalline state as opposed to the amorphous state. Native cotton, for example, has a very high proportion of crystalline cellulose and is therefore difficult to saccharify.
It is known that a true cellulase will saccharify even native cotton. Such cellulases are secreted by certain fungi and bacteria. The cellulase of the fungus Trichoderma reesei has been found to have a particularly high saccharification activity. Significantly, the activity is retained in cell-free filtrates containing the cellulase. The cellulase of T. reesei is therefore used as an industry standard in measuring relative saccharification.
The anaerobic, thermophilic bacterium Clostridium thermocellum has heretofore been believed to have only limited saccharification activity. The extracellular fluid of this species contains carboxymethyl-cellulase, an enzyme reported to have weak activity which is oxygen-stable and unaffected by Ca.sup.2+ with respect to saccharification of crystalline cellulose. Generally, the extracellular bacterial cellulases do not exhibit the extensive saccharification of crystalline cellulose characteristic of the extracellular fungal cellulases. However, as the bacteria may grow more rapidly than the fungi on either amorphous or crystalline cellulose, it would be desirable to increase the saccharification activity of the extracellular bacterial cellulases, and in particular the cellulase of C. thermocellum.